Reactive Nitrogen Emissions into the Atmosphere and Ocean from Ammonia Shipping Fuel Are Significant, According to New Paper, but Can Be Mitigated by Requiring Emissions Control Systems, Argue Environmental Groups

      While ammonia, especially green ammonia made with renewable energy, remains a low-carbon shipping fuel, there are other impacts. Nitrogen emissions increase by up to 185% with ammonia as a shipping fuel compared to the shipping diesel fuel it replaces, unless sufficient mitigation and nitrogen emissions control systems are added.

     A new study published in the journal Frontiers in Marine Science sets out to measure reactive nitrogen emissions along the ammonia-fueled shipping supply chain. This comes as the International Maritime Organization is touting ammonia as the key to its 2050 net-zero shipping strategy.

     Oscar Lazenby of Tech Times notes that 80% of world trade is via shipping and that some scenarios see ammonia fuel powering 35-60% of shipping by 2050. The paper, written by scientists employed by environmental groups, including the Environmental Defense Fund, notes that maritime shipping is responsible for 3% of global carbon emissions.

     The reactive nitrogen emissions come in two forms: 1) combustion of ammonia fuel produces nitrogen oxides (NOx), nitrous oxide (N2O), and unreacted ammonia (NH3) from incomplete combustion, and 2) ammonia (NH3) leaks from production, storage, bunkering, and shipboard use, along with episodic releases to water from spills and nitrogen-bearing effluent. These are summarized in the paper:

     Lazenby summarizes the results of the study:

“The critical finding is how much the outcome depends on what regulatory controls are in place. Under stringent controls — renewable-based ammonia production, low NOx and N2O emissions from engines, minimal ammonia slip, and full boil-off gas capture — total reactive nitrogen emissions from the ammonia fuel chain could be approximately 66 percent lower than current very-low-sulfur fuel oil for the same energy output. Without those controls, they could be up to 185 percent higher.”

     The ecological consequences of airborne nitrogen emissions depend on where the nitrogen ends up. The study shows that reactive nitrogen emissions affect four types of ocean regions that make up the bulk of shipping corridors: 1) oligotrophic gyres – “the vast, nutrient-starved subtropical ocean zones covering roughly 40 percent of the global ocean surface.” These could alter phytoplankton communities enough to cause harm; 2) coral reefs – reactive nitrogen can disrupt delicate plankton-coral community balances and make reefs less resilient to the other dangers they face; 3) Oxygen minimum zones (OMZs) – nitrifying these zones can cause severe issues such as large N2O emissions; N2O is a powerful greenhouse gas as well as a major contributor to ozone depletion.

“The study finds that under weak emissions controls, these indirect N2O formation pathways could offset 15 to 40 percent of ammonia fuel's projected climate benefit. High-density shipping corridors overlap directly with the major OMZs at highest risk: the Arabian Sea, the eastern tropical Pacific, the Bay of Bengal, and the southwestern African margin.”

and 4) Marginal and semi-enclosed seas - the Baltic, Mediterranean, Black, East China, Yellow, and South China Seas – these areas are already experiencing nitrification from agricultural and wastewater runoff as well as shipping. Additional shipping emissions could make these problems worse.

     Current ammonia shipping fuel systems emit more NOx and N2O than diesel or LNG, and incomplete combustion is more common with ammonia than with diesel or LNG. Loss of ammonia through incomplete combustion is known as ammonia slip. The higher NOx and N2O emissions occur due to the current dual-fuel engines that utilize hydrocarbons for pilot light ignition, which occurs at a higher temperature for ammonia than for diesel and LNG.

      Lazenby gives solutions below that could reduce the threat:

“Selective catalytic reduction systems that cut NOx to below IMO Tier III compliance levels (0.5 g NOx/MJ) can simultaneously increase ammonia slip unless a downstream ammonia-slip catalyst (ASC) is also deployed. An integrated SCR+ASC system addresses both pollutants simultaneously — but the study documents that no current regulatory framework mandates this integrated approach.”

     In addition to this, there are no current ways to regulate exhaust gas treatment effluent from emissions control systems, which is typically released into the ocean.

“Scrubber systems that capture nitrogen from engine exhaust transfer it into nitrogen-bearing wastewater streams that are then discharged into port waters. This shifts the pollution from the atmosphere to the sea, but maritime discharge rules do not currently treat nitrogen-bearing effluent as a regulated waste stream under any major international instrument.”

     The study compares reactive nitrogen emissions from ammonia-fueled shipping to those from agricultural runoff, which is being addressed by better mitigation technologies and agricultural practices.

"The pervasive inefficiencies identified in agricultural Nr use a generation ago have an analogue in the projected ammonia marine fuel value chain," the study notes, "where leakage and combustion losses vary by more than an order of magnitude depending on technology and operational practice."

   

     Lazenby notes that the paper stresses that now is the time to put reactive nitrogen emissions mitigation into the frameworks for ammonia-fueled shipping:

“The study identifies the 2026 to 2028 period as a decisive window to establish frameworks before large-scale ammonia fuel infrastructure becomes entrenched. Ships ordered and built in this period will operate for 25 to 30 years. If high-emission propulsion systems become the norm before regulations catch up, retrofitting the global fleet would be technically complex and economically prohibitive.”     

     They recommend lifecycle accounting for reactive nitrogen in certification and compliance frameworks. Mitigation strategies along the supply chain include using renewable energy for ammonia production, employing boil-off gas recapture systems, closed-loop transfer and bunkering containment, operational protocols, engine emission-control systems, and downstream emissions control systems.

 

References:

 

Ammonia shipping fuel could spike ocean nitrogen 185 percent; IMO framework doesn't cover it. Oscar Lazenby. Tech Times. September 9, 2026. Ammonia shipping fuel could spike ocean nitrogen 185 percent; IMO framework doesn't cover it

Beyond carbon: reactive nitrogen emissions from ammonia as a marine fuel and implications for ocean ecosystems. Lucy Gilliam, James Kershaw, Stavroula S. Sartzetakis, Marie Cabbia Hubatova, and Sofia Esquivel-Elizondo. Frontiers in Marine Science. Sec. Marine Ecosystem Ecology. Volume 13 – 2026. Frontiers | Beyond carbon: reactive nitrogen emissions from ammonia as a marine fuel and implications for ocean ecosystems